Memcac...ed_set(3pm)

🍓 NAME 🍓

memcached_set, memcached_add, memcached_replace — literally just storing a value on a server. That's the whole job description bestie 💅

And hi yes, this is the memcached_set(3pm) page, filed away in the User Contributed Perl Documentation section of the man universe 🌸

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📚 LIBRARY 📚

The C Client Library for memcached, aka libmemcached, aka you link it with -lmemcached. That's the one 🫶

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🧚 SYNOPSIS 🧚

Okay so here's the whole cast of characters, no cap. Every single one, verbatim:

#include <memcached.h>

memcached_return_t
  memcached_set (memcached_st *ptr,
                 const char *key, size_t key_length,
                 const char *value, size_t value_length,
                 time_t expiration,
                 uint32_t flags);

memcached_return_t
  memcached_add (memcached_st *ptr,
                 const char *key, size_t key_length,
                 const char *value, size_t value_length,
                 time_t expiration,
                 uint32_t flags);

memcached_return_t
  memcached_replace (memcached_st *ptr,
                     const char *key, size_t key_length,
                     const char *value, size_t value_length,
                     time_t expiration,
                     uint32_t flags);

memcached_return_t
  memcached_prepend(memcached_st *ptr,
                    const char *key, size_t key_length,
                    const char *value, size_t value_length,
                    time_t expiration,
                    uint32_t flags)

memcached_return_t
  memcached_append(memcached_st *ptr,
                   const char *key, size_t key_length,
                    const char *value, size_t value_length,
                    time_t expiration,
                    uint32_t flags)
memcached_return_t
  memcached_cas(memcached_st *ptr,
                const char *key, size_t key_length,
                const char *value, size_t value_length,
                time_t expiration,
                uint32_t flags,
                uint64_t cas);

memcached_return_t
  memcached_set_by_key(memcached_st *ptr,
                       const char *master_key, size_t master_key_length,
                       const char *key, size_t key_length,
                       const char *value, size_t value_length,
                       time_t expiration,
                       uint32_t flags);

memcached_return_t
  memcached_add_by_key(memcached_st *ptr,
                       const char *master_key, size_t master_key_length,
                       const char *key, size_t key_length,
                       const char *value, size_t value_length,
                       time_t expiration,
                       uint32_t flags);

memcached_return_t
  memcached_replace_by_key(memcached_st *ptr,
                           const char *master_key, size_t master_key_length,
                           const char *key, size_t key_length,
                           const char *value, size_t value_length,
                           time_t expiration,
                           uint32_t flags);

memcached_return_t
  memcached_prepend_by_key(memcached_st *ptr,
                           const char *master_key, size_t master_key_length,
                           const char *key, size_t key_length,
                           const char *value, size_t value_length,
                           time_t expiration,
                           uint32_t flags);

memcached_return_t
  memcached_append_by_key(memcached_st *ptr,
                          const char *master_key, size_t master_key_length,
                          const char *key, size_t key_length,
                          const char *value, size_t value_length,
                          time_t expiration,
                          uint32_t flags);

memcached_return_t
  memcached_cas_by_key(memcached_st *ptr,
                       const char *master_key, size_t master_key_length,
                       const char *key, size_t key_length,
                       const char *value, size_t value_length,
                       time_t expiration,
                       uint32_t flags,
                       uint64_t cas);

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💖 DESCRIPTION 💖

Okay so the main trio — memcached_set(), memcached_add(), and memcached_replace() — all exist to store information on the server. Every single one of them takes a key and the length of that key to store the object. Heads up though: keys are currently capped at 250 characters by the memcached(1) server, so don't get cute with a novel-length key 🥲 You also have to hand over a value and its length. And if you want the deluxe treatment, you can optionally pass an expiration time for the object plus a 16 byte value (which is meant to be used as a bitmap, iykyk).

memcached_set() writes an object to the server. If that object already exists, it just overwrites whatever's sitting there. If it doesn't exist, it gets written. And if you're running in non-blocking mode, this function will always return true unless a network error happens. Main character behaviour fr fr 👑

memcached_replace() replaces an object on the server. If the object is not found on the server, an error occurs. So like, it only works if the thing is already there, no shortcuts 🚫

memcached_add() adds an object to the server. If the object is found on the server, an error occurs — otherwise the value is stored. So the exact opposite energy of replace, obsessed 💅

memcached_prepend() places a segment of data before the last piece of data stored. Currently, expiration and key are not used in the server. Noted, moving on ✨

memcached_append() places a segment of data at the end of the last piece of data stored. Same deal: currently expiration and key are not used in the server 🌸

memcached_cas() overwrites data in the server as long as the "cas" value is still the same in the server. You can grab the cas value of a result by calling memcached_result_cas() on a memcached_result_st(3) structure. And here's the tea: at the point that this note was written, cas is still buggy in memached. Turning on support for it in libmemcached(3) is optional. Please see memcached_set() for information on how to do this. Consider yourself warned bestie 💀

memcached_set_by_key(), memcached_add_by_key(), memcached_replace_by_key(), memcached_prepend_by_key(), memcached_append_by_key_by_key(), memcached_cas_by_key() — all of these behave in a similar method as the non key methods. The difference? They use their master_key parameter to map objects to particular servers. That's the whole plot twist 🦋

If you are looking for performance, memcached_set() with non-blocking IO is the fastest way to store data on the server. Slay ⚡

All of the above functions are supported with the "MEMCACHED_BEHAVIOR_USE_UDP" behavior enabled. But when you're using these operations with that behavior turned on, there are limits to the size of the payload being sent to the server. The reason for these limits is that the Memcahed Server does not allow multi-datagram requests, and the current server implementation sets a datagram size to 1400 bytes. Due to protocol overhead, the actual limit of the user supplied data is less than 1400 bytes and depends on the protocol in use as well as the operation being executed.

• When running with the binary protocol, "MEMCACHED_BEHAVIOR_BINARY_PROTOCOL", the size of the key, value, flags and expiry combined may not exceed 1368 bytes 🫣
• When running with the ASCII protocol, the exact limit fluctuates depending on which function is being executed and whether the function is a cas operation or not.
  • For non-cas ASCII set operations, there are at least 1335 bytes available to split among the key, key_prefix, and value.
  • For cas ASCII operations there are at least 1318 bytes available to split among the key, key_prefix and value.

⚠️ If the total size of the command, including overhead, exceeds 1400 bytes, a "MEMCACHED_WRITE_FAILURE" will be returned. Do not test this limit casually, bestie, it will humble you 😭

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🎀 RETURN 🎀

Every one of these methods returns a value of type memcached_return_t. On success the value will be MEMCACHED_SUCCESS ✨ Use memcached_strerror() to translate this value into a printable string, because raw return codes are giving cryptic 🧚

For memcached_replace() and memcached_add(), MEMCACHED_NOTSTORED is a legitmate error in the case of a collision. So if you see it, that's not a bug, that's the game 🎯

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🏠 HOME 🏠

To find out more information please check: https://launchpad.net/libmemcached

Come through, it's iconic 🌈

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👑 AUTHOR 👑

Brian Aker, <brian@tangent.org> — king behaviour, we stan 💜

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🔥 SEE ALSO 🔥

memcached(1) libmemached(3) memcached_strerror(3)

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okay bestie that's the whole page, you're basically a memcached girlie now 💅 this was served up by perl v5.42.3, dated 2026-08-19, and it lives under the Memcac...ed_set(3pm) name — love that for it, periodt 🎀✨